The present invention relates generally to welding, and more particularly to a method for resistance welding a tube to a member.
Resistance welding (also known as electric-resistance welding) is a known metallurgical process used to weld a right-angle end flange of a tube to a surface projection of a plate wherein metal is heated by its own resistance to a semi-fused (i.e., soft) or fused (i.e., molten) state by the passage of very heavy electric currents for very short lengths of time and then welded. In one known variation, the plate is stamped creating depressions on the top surface and creating surface projections on the bottom surface so that during the resistance welding, the projections soften and/or melt creating a weld nugget which joins together the plate to the tube flange.
Conventional methods for welding a tube to another tube or for welding a tube to a plate include gas metal arc welding. Gas metal arc welding uses a consumable metal wire as one electrode and the parts as another electrode, and moves the consumable metal wire (or the parts) to draw an arc and weld the parts together. The welding is accompanied by a gas (such as a mixture of argon and carbon dioxide) to prevent oxidation and stabilize the arc. Such gas metal arc welding is well known. In a conventional gas metal arc welding technique, solid metal wire or metal core wire (i.e., an annular-solid wire whose core is filled with metal powder such as a mixture of metal, alloy and/or oxide powders) is used with the wire at a positive electrical welding potential and with the parts electrically grounded. The welding arc creates a molten weld puddle which results in the welding together of the parts. A ceramic ferrule is used to contain the weld puddle when needed. Gas metal arc welding requires expensive welding equipment, the molten weld puddle tends to flow away from the joint area (depending on the joint position with respect to gravity) resulting in welds of inconsistent quality, and the process requires a long cycle time between welds.
Conventional methods for attaching parts together also include friction welding. To join two tubes together end to end, one of the tubes is rotated about its longitudinal axis, and the tube ends are pressed together, wherein friction causes heating of the ends creating the weld. To join a tube to a plate, the tube is rotated about its longitudinal axis, and the tube end and the plate are pressed together, wherein friction causes heating creating the weld. Friction welding requires expensive welding equipment, and the process requires a long cycle time between welds. Friction welding is not easily applicable to thin-walled tubes because they do not retain their shapes well under heat and pressure. It is noted that laser and electron-beam welding for the above joints also need expensive equipment and expensive joint preparation.
What is needed is a less expensive method for metallurgically joining a tube to a member.
A first method of the invention is for resistance welding a tube to a member and includes steps a) through d). Step a) includes obtaining a tube having an axially-extending first portion and having a tube form which extends transversely from the first portion, wherein the tube form includes at least one axial projection. Step b) includes obtaining a member. Step c) includes, after steps a) and b), positioning the tube and the member with the at-least-one axial projection contacting the member. Step d) includes, after step c), creating a resistance welding current path through the member and the tube including the at-least-one axial projection creating a weld zone which includes at least some of the at-least-one axial projection and at least some of the member.
A second method of the invention is for resistance welding a tube to a member and includes steps a) through d). Step a) includes obtaining a tube having an axially-extending first portion and having a tube form which extends transversely from the first portion, wherein the tube form includes at least one axial projection. Step b) includes obtaining a member. Step c) includes, after steps a) and b), positioning the tube and the member with the at-least-one axial projection contacting the member. Step d) includes, after step c), creating a resistance welding current path through the member and the tube including the at-least-one axial projection and relatively axially moving the at-least-one axial projection deformingly against the member creating a weld zone which includes at least some of the at-least-one axial projection and at least some of the member.
Several benefits and advantages are derived from one or more of the methods of the invention. The tube form allows resistance welding of a tube to a member to be commercially feasible, as can be appreciated by those skilled in the art. The at-least-one axial projection enables the welding of thick-thin part combinations and allows a smaller welding current to be used since all of the welding current creating the weld zone flows only through the projection(s) and not through a larger area. Resistance welding is less expensive than gas metal arc welding or friction welding. Resistance welding also has a shorter cycle time between welds than gas metal arc welding or friction welding.